Woven papermaker fabrics are intended to be used in the sections of a paper making machine as a support for the paper web. They are endless woven fabrics or fabrics made endless by means of a seam which circulate in the paper making machine. In the first section of a paper making machine, forming fabrics are used, on the top strand of which a paper pulp is disposed at the start, and the latter is dewatered through the forming fabric such as to form a paper web, wherein the dewatering is supported in particular by suction boxes disposed on the under or inner side of the fabric.
A papermaker fabric must have a fine structure on the paper side in order to support and retain a high percentage of the deposited paper fibers. On the other hand, the machine side of such a fabric must be durable enough to withstand wear and give adequate life, strong enough to resist tensile forces and open enough to provide drainage. Meeting these criteria generally requires that at least two fabric layers are superimposed utilizing threads of different size and/or count per cm and differing weave patterns.
Generally known are three types of papermakers fabrics used for the forming section of a papermaker machine. A first type is constructed of an upper and a lower layer out of transverse threads, the threads of both layers are superposed in pairs. The fabric layers are connected by longitudinal threads mostly interwoven in the upper layer and only a portion of them additionally interwoven in the lower layer, the threads of which are preferably of a larger thickness than the longitudinal threads. Such kind of forming fabrics are commonly called double-layer fabrics.
The second type of fabrics is created from two distinct fabrics, one having the qualities desired for the paper side and the other the qualities desired for the machine side. The two fabrics are stitched or bound together by additional or independent binding yarns, which do not belong to the recurring woven fabric repeats formed by the longitudinal and transverse threads of both layers. This type of papermaker fabric is commonly called a triple-layer fabric.
The third type of papermaker fabric is based on the second type, i.e. has two distinct fabric layers comprising longitudinal and transverse threads interwoven with one another respectively. Unlike the triple-layer fabrics, this type of fabric has no additional or independent binder threads. The connection of the two layers is made of their own threads, i.e. by so-called “structural”, “intrinsic” or “fabric-born” threads. These are threads which are an integral part of the weave pattern of the fabric or its woven fabric repeats. Composite fabrics of these types are commonly called SSB (sheet support binder) fabrics.
The differences between the foregoing three types of fabrics are also described in U.S. Pat. No. 5,152,326, columns 1 and 2, U.S. Pat. No. 5,052,448, columns 1 through 3 and U.S. Pat. No. 4,554,953, columns 1 through 3.
Papermaker fabrics of the SSB composite type are known, wherein the connection between the two layers is achieved by a number of structural binding thread pairs, the binding of the one binding thread in one layer is continued by the other binding thread of the binding thread pair, if the one binding thread changes from one layer to the other layer in a symmetrical manner (U.S. Pat. No. 5,152,326, US 2008/0035230 A1, EP 1 605 095 A1 and EP 1 365 066 A1). Also known are embodiments of composite papermaker fabrics, wherein the two layers are connected by structural binder threads belonging to the first woven fabric layer (U.S. Pat. No. 5,052,448; U.S. Pat. No. 4,554,953; EP 2 314 762 A1, U.S. Pat. No. 4,564,051, JP 49010281 B, DE 298 07 274 U1 and EP 1 365 066 A1). In the latter document, an embodiment is also disclosed, wherein the two layers are connected by binding threads of the second woven fabric layer forming the machine side layer.
In the figures of JP 62078294 A, a papermaker fabric is disclosed having a first woven fabric layer provided for the paper side and made of first longitudinal and first transverse threads interwoven with one another and having a second woven fabric layer provided for the machine side made of second longitudinal and second transverse threads interwoven with one another. The two woven fabric layers are connected to one another by binder threads at binder points formed by structural second threads running along and below associated first threads.
Both the binder threads and the associated first threads bind first threads of the first woven fabric layer running transversely thereto at the binder points on their paper side wherein the binder threads and also the first threads form knuckles at the binder points. The knuckles of the binder threads have peaks on their paper side, all of which constitute a peak plane parallel to the paper side. The knuckles of the associated first threads have concave inner bends, the points of which lying nearest to the paper side constitute an inner plane parallel to the paper side. The tension of the first thread extending transversely to the binder threads is such that the inner plane as defined above is nearer to the paper side or at most in the same level as the peak plane so that respectively, the binder threads and the associated first threads are forming superimposed pairs also at the binder points.